In 3GPP cellular networks it is possible to guarantee resources through a guaranteed bit rate, GBR, but also to provide additional resources when available but limited by a maximum bit rate, MBR, which can be utilized by adaptive applications. The MBR is set to be smaller or the same as the GBR, that is, MBR≦SBR. However, the application needs support to set the initial rate correctly and also to switch down the rate in time in case of degraded service conditions from the network. In some scenarios, it may also be preferred to upgrade the rate in case the service conditions are again improving.
When doing a handover to a heavily/less loaded cell or by an Inter Radio Access Technology, IRAT, handover to a Radio Access Technology, RAT, with a lower/higher capability the service offered by the Radio Access Network, RAN, can be changed abruptly. If the application does not get a notification about this in advance it runs the risk of heavily degraded user service performance. Even though the application may be able to recover over time, such abruptions should be avoided. One such example may be where an mobile station/user equipment, MS/UE, with an active Voice over IP, VoIP/IP Multimedia Subsystem, IMS, call is moving from LTE coverage to 2G RAN, i.e. GSM EDGE Radio Access Network, GERAN, coverage.
If no explicit congestion notification is given to the application, it will be notified implicitly by experienced packet drops. However, this is not acceptable for several applications, e.g. a video service would be stalled or the like.
One example on how to notify an application explicitly about increased risks for congestion in the network, before congestion happens, is to use the Explicit Congestion Notification (ECN) on the IP layer. When getting the ECN indication the application in the receiver can use application layer signaling to ask the sender to lower the send rate and by that avoid packet losses. However, a handover will in some cases give additional delays and sometimes also buffering. This impairs the possibility to adjust the rate based on the ECN indication.